Anti-aliasing is used to improve the appearance of graphical elements on computer screens. Without anti-aliasing, edges of graphical elements can appear jagged. Anti-aliasing can reduce the perceived jaggedness of the edges.
When an image is upscaled to a higher resolution, anti-aliased elements in the upscaled image can become blurred and artifacts can become visible. Consider an image of a road map that contains a number of anti-aliased graphical elements (e.g., streets, street names). While maps provided by leading Internet sites have sufficient resolution (72 ppi) to look fine on a computer screens, this resolution is not high enough for printing on standard printers, even with standard paper. Therefore, when viewed on a computer screen, edges of these anti-aliased elements appear sharp. When the elements are printed, however, edges in the print appear blurred. Many people mistakenly assume that their printers are of low quality, because their printers are “unable” to reproduce the visual quality perceived on the computer screens. In fact, the difference in perceived quality on the screen and quality of the print is due to the combination of the usually higher resolution power of the printer and paper media with the relatively low resolution of the map content.
It would be desirable to upscale anti-aliased graphical elements, while retaining perceived image quality.